Hydraulic regulator with hydraulic restoring and stabilizing device



June 15, 1954 M. A. EGGENBERGER 2,681,044 HYDRAULIC REGULATOR WITHHYDRAULIC RESTORING AND STABILIZING DEVICE Filed June 24, 1952 3/1, 0 3o o a 9G a a /0d m 46 u 26d 11261111: W4 :zZ:

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-95 /9 2/ L 2a 22 4 24 d Z-i$155i' 1 DRRIN HIGH PRESS.

O STEAM CONDENSER FROM BO R Invehtor:

Ta I a e His Attorney- Patented June 15, 1954 HYDRAULIC REGULATOR WITHHYDRAULIC RESTOR-ING AND STABILIZING DEVICE Markus A. Eggenberger,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application June 24, 1952, Serial No. 295,260

4 Claims.

This invention relates to hydraulic servomechanism, particularly to ahydraulic-mechanical device for overcoming inherent instability in ahydraulic regulator used to control the steam supply to the shaftpacking seal of a steam turbine type of prime mover.

As will be appreciated by those skilled in the art relating to hydraulicservo-mechanisms, the tendency of a servo to become unstable and huntbecomes greater as the regulation of the mechanism approaches zero,regulation being the change occurring in the condition sensed as thecondition being governed changes from its minimum value to its maximumvalue. Many expedients have been employed in the prior art to achievestability when the regulation of the servo equals or approaches zero, orbecomes negative. One such expedient is a liquid-filled dashpot, asshown for instance in the patent to Dettenborn2,077,38l, issued April20, 1937, and Warren-2,113,416, issued April 5, 1938, both assigned tothe same assignee as the present ap .plication.

A further improved hydraulic arrangement for better stability of aservo-mechanism used to control the flow of steam to the shaft packingsof a steam turbine is disclosed in my U. S. Patent No. 2,635,639, issuedApril 21, 1953, and assigned to the same assignee. The present inventionis a still further improvement of that hydraulic stabilizingarrangement.

Accordingly, the object of the present invention is to provide animproved hydraulic-mechanical stabilizing device for servo-mechanisms ofthe type described which gives even greater stability than the system ofmy copending application.

A further obiect is to provide hydraulic servomechanism of the typedescribed for effecting stable operation with zero regulation.

A still further object is to provide an improved hydraulic servostabilizing device which, in the event of a sudden change in thecondition being sensed, will vprovide instantaneously a rate of responsesubstantially greater than that which is efiected. when the conditionchange takes place more slowly.

Other objects and advantages will become apparent from the followingdescription taken in connection with the accompanying drawing, in whichthe single figure represents diagrammatically hydraulic servo-mechanismhaving a stabilizing device incorporating the invention.

Generally, the invention is practiced by adding to the stabilizingdevice of myv above-identified Patent 2,635,639, a special hydraulicrestoring arrangement, eliminating the mechanical feedback system andacting directly on the hydraulic stabilizer in such a way that the speedof response of the mechanism is increased in the case of a large andfast change in the condition being controlled.

Referring now more particularly to the drawing, the hydraulic regulatorindicated generally at I is arranged to receive high pressure steam froma boiler (not shown) through conduit 2 and supply it at a very muchlower preselected pressure to the steam-sealed shaft packings (notshown) by Way of conduit 3.

The pressure regulator I is arranged generally like the steam sealregulators previously known, having a signal output rod member 4positioned by a conditionresponsive device 5 arranged to control thepilot valve E'of a hydraulic motor I so as to actuate a dual'steamregulating valve, which admits steam through a valve 8, or,alternatively, dumps steam to the condenser by opening a second valve 9.

This invention particularly relates to the special hydraulic stabilizingdevice H), which modifies the forces applied to the condition-responsivemember A in orderto achieve the required degree of stability.

As shown in the drawing, the condition-responsive device 5 comprises a.housing H defining a pressure chamber I2 to which is communicated spring4a engaging an abutment ib carried by the rod. The upperend of spring4a, engages a threadedcap member to which may be screwed down farther orretracted to vary the force which spring 4a. exerts on the rod 4. Thelower end of rod 4 is secured to'a first disk member M, the

lower surface of which is subjected to the signal pressure in chamber:2; To the outer circumference of disk I4 is sealed a flexible bellowsmember i5 cooperating with an inner bellows member I6 to define a firstannular expansible chamber I1. The upper ends of bellows IS, IS aresealed to the housing I I.

The annular chamber I1 is filled with a hydraulic liquid, such as asuitable petroleum oil, which liquid is communicated by way of conduitl8 with the hydraulic stabilizer l9. It will be seen that, sincethespace withinlbellows l6 communicates with the atmosphere by way ofthe-substantial clearance space around rod 4,

the disk H5 is positioned against the bias of spring 4a by the steampressure in chamber I 2 acting on an annular area of the disk, asmodified by any liquid pressure occurring in the chamber H.

The hydraulic stablilizer i6 comprises a housing lila which may beconveniently formed with end closure members iilb, I00. Adjacent themidportion of the housing is a disk member I9 defining a large centralopening 26 around which is sealed one end of a flexible bellows 2 I. Theother end or" the bellows is sealed to a floating disk 22, the neutralposition of which is determined by two opposed coil springs 23, 24. Itwill be seen from the drawing that the interior of bellows 2| is in freecommunication, by way of the generously proportioned opening with thechamber above disk I9.

Slidably disposed. in the upper portion of housing Eta is a pistonmember 26. A by-pass conduit 2'! containing a needle valve 28communicates liquid from the space 25 at the lower side of piston 26 tothe chamber 29 defined above piston 26. As shown in the drawing, thenormal level of oil in chamber 29 is well above the port 21a, and thesurface of the liquid in chamber 29 is freely vented to the atmosphereby way of the vent Hid.

As will be apparent from the drawing, conduit [8 freely communicateshydraulic oil from annular chamber I? to chamber 25 in the stabilizerl0, and by way of opening 20 to the interior of bellows 2|, whileconduit 21 communicates liquid past the needle valve 28 to the space 29above piston 26. This chamber 29 serves as a storage reservoir forhydraulic liquid displaced from chamber 25 and also serves to keep theconnecting conduits full of liquid at all times. This is why the port27a must be below the lowest normal level of the liquid in space 29.

It is to be noted that the piston 26 is provided with a pair ofoppositely acting check-valve disk members 26a, 25b, held against theirseats by coil springs 25c, 26d, respectively. It will be apparent fromthe drawing that excessive pressure in chamber 25 will cause thecheck-valve disk 26:! to rise against the bias of its spring permittingliquid to flow directly into chamber 29, while a sudden reduction ofpressure in chamber 25 will cause check-valve 26b to open against theforce of its spring 2501 so as to admit liquid from chamber 29 intochamber 25. The function of these checkvalves will be noted hereinafter.

As contrasted with the mechanical restoring arrangement disclosed in myPatent 2,635,639, the present arrangement includes hydraulic restoringmeans in the form of a feed-back lever 3| carried on a pivot 31a bymeans of the fulcrum 3H) and link 3lc. The left-hand end of lever 3| ispivoted at 32 to the upper end of piston rod and the right-hand end ofthe lever is pivoted at 33 to the upper end of piston rod 917 by meansof link 33a.

With further reference to the steam control valves 8, 9, it will be seenthat the hydraulic motor piston rod 917 carries an abutment member 90engaging the forked left-hand end portion 34a of a lever 34. The steamdump valve disk 9a is positioned directly by the double-acting hydraulicmotor I. It is to be noted that the outer diameter of the valve diskmember 9a is equal to that of the valve seat with which it cooperates,so that disk 9a is capable of being displaced downwardly below theposition shown in the drawing, corresponding to the dotted line position911 of the abutment member 90. The steam admission valve 8 has a flowcontrol disk member 8a which is biased downwardly by a coil spring 81)into engagement with a conical seat member, as long as abutment 93 doesnot engage the forked end 3411 of lever 34. The inlet valve stem ispivoted at 3417 to the right-hand end of lever 34.

With this arrangement, it will be apparent that, upon upward movement ofhydraulic motor piston rod 917, the abutment 9c merely moves away fromthe lever end portion 34a, and the valve disk 9a rises to open the dumpport. Conversely, upon downward movement of piston rod 92), abutmentengages lever end portion 3 ia so as to raise valve disk 8a and open thesteam inlet. Such downward movement of piston rod 91) of course causesthe valve disk 9a to move downwardly into its port.

The operation of this improved regulator may be outlined as follows:Assume first that the needle valve 28 is wide open. If now the steampressure in conduit 3 should suddenly increase, the pressure responsivedisk It will move upwardly against the downward force of spring 4a,substantially unafiected by the liquid in chamber I1, which liquid ismerely displaced through conduit l8 and by way of by-pass conduit 21 tothe generously proportioned reservoir space 29 above piston 25. Thus,except for a comparatively small amount of hydraulic damping eifected bythis flow of liquid from chamber IT to chamber 29, the pilot valve 6 ismoving in very much the same way as in the device of my prior copendingapplication, but, since no positive feed-back from the hydraulic motorpiston m to the pilot valve is present, the piston Ia would go on movingas long as the pilot valve 6 stays on port, that is, as long as thepressure in chamber I2 is different from the value which holds the rod 4in a position as to put the pilot valve 6 on port. This system would beinherently unstable;

In order to make this system stable, the special action of the hydraulicstabilizer i8 is brought into action. To do this, the needle valve 28 ispartly closed. If now an increase in the steam pressure occurs, the diskIt will move upward as described previously, causing the pilot valve tomove off port and piston Ia to rise, operating valves 8a or 911., as thecase may be, toward the position required by the changed steam flowwhich caused the steam pressure change. At the same time the upwardmovement of stem Qb causes the feed-back lever 3| to pivotcounterclockwise about its fulcrum 31a, which motion causes the piston26 to descend. This pushes the floating disk 22 downwardly against thebias of spring 24, increasing the fluid pressure in charm ber 25, whichis communicated by conduit 18 to the chamber 11. Thus disk 14 is pushedback down, restoring pilot valve 6 so as to stop the movement ofhydraulic motor 7. At the same time, the increased pressure in chamber25 effects a restricted flow of oil through conduit 2! and past needlevalve 28, and this flow causes some decrease in the pressure in chamber25. This small decrease in pressure tends to allow disk M to riseslightly again, and the pilot valve 8 tends to admit liquid to motor 1for positioning the valve stem 96 upwardly.

The net eifect of all these interacting factors is that the steam valves8a and/or 9a are caused to slowly approach the position required for thenew steady-state condition; and, at the time, the liquid pressure inchamber 25 has become equalized with the atmospheric pressure in chamber29 and the pressure of the shaft sealing steam conduit 3 has returnedexactly to 5. the preselected steady-state value, but with an increasedsteam flow through the dump valve 9 and/or a decreased flow throughinletvalve 3.

Since, with no positive pressure in the liquidfilled chamber 57,. thereis only one steam pres sure in chamber [2 which will balance the forceof spring 4a, with pilot 8 in the aligned or on port position, the netregulation of the system is zero, meaning that the steady-state pressurein conduit 3 is constant, regardless of the rate of steam flow; and thisis true over the full range of operation, regardless of whether theinlet valve 8 is admitting steam to the conduit 3 or the dump valve 9 isreleasing steam to the condenser.

Upon a drop of the steam pressure in conduit 3 below the preselectedvalue, the operation of the system is the reverse of that describedabove. That is, the decreased pressure in chamber i2 causes clisl; hi todescend, hydraulic pilot ii causes the motor 7 to move the valve stem8?; downwardly so as to close the dump valve 9d, and/or to open thesteam inlet valve 8a. Meanwhile the upward motion of piston 26 causesthe floating disk 22 to rise against the bias of spring 23, producing adrop in pressure in chambers 25 and I! which has a hydraulic restoringefiect on the disk Hi. The gradual bypassing of liquid through conduit27 makes the mechanism approach slowly the new steady-state condition asdescribed above.

An additional stabilizing efiect, as fully disclosed. in my priorpatent, is also present in the above-described system. This effect is asfollows. An increase of the steam pressure in chamber I2, causing thedisk M to move up, tends to decrease the combined volume of chambers I!and 25, forcing the floating disk 22 to move down against the bias ofspring 24, thereby increasing the pressure in chambers 25 and H. Thistends to reduce the amount of motion transmitted to rod 3 for a givenpressure change in chamber l2. This increases the instantaneousregulation, which is the necessary transient pressure change sensed asthe rate of steam flow from or to the conduit 3 changes by a certainpredetermined amount within a certain short time. As will be appreciatedby those skilled in the art relating to servo-mechanisms, an increaseinthe instantaneous regulation improves the stability of a control systemof the type described.

It remains to note the effect of the springbiased check valves 26a, 25bassociated with the feed-back piston 26. One function of these reliefvalves is to prevent mechanical damage to the bellows i5, i6, 2i due toexcessive pressures. It will be observed that an excessive suddenmovement of piston 26 could produce a very high or a very low pressurein chamber 25. This will cause one or the other of these relief valvesto open, thus interchanging liquid with the chamber 23 so as to insurethat such excessive pressures will not be sufficient to cause mechanicaldamage to the respective bellows.

An equally important function of the check valves is that they increasethe speed of response of the mechanism to sudden large changes inpressure of the steam. It will be apparent, from a consideration of thedrawing, that opening of either check-valve 26a or 26b has the sameeffect as opening the needle-valve 28. Thus the springloaded reliefvalves in piston 26 have the same efiect as if the needle valve 28 wereautomatically opened whenever the pressure change in chamber 25 exceedspreselected values. The advantage of having the two relief valves isthat the respective'springs 260, 261) can be so selected as to havedifferent stiffness, so that the response is different for increase inpressure in chamber 25, as compared with that occurring when there is asudden decrease in pressure. Specifically, the spring 25:: may beselected so that valve .2601, requires a pressure differential of 3pounds per square inch to open it, whereas valve 2% requires adifferential of only about 3 pounds per square inch to unseat it.

It will be seen that the invention involves the interrelation of asubstantial number of hydraur lic-mechanieal effects, which cooperate toeifect a substantial improvement in the stability and responsecharacteristics of the system. At the same time, the improved system isdesigned to operate with zero steady-state regulation, so thatthesteady-state pressure in the conduit 3 is always exactly the sameregardless of the rate of steam how. The substitution of the hydraulicfeed-back effect further contributes to the stability and rate ofresponse; and the check-valves in the feedback piston renders the systemmore versatile by providing means for obtaining a somewhat differentresponse upon a sudden large increase in steam pressure compared withthat occurring upon a sudden decrease in pressure.

It will be apparent that the showing of the preferred embodiment in thedrawing is intended to be diagrammatic only, and that in an actualstructure the mechanical details may take many different forms. it is ofcourse intended to cover by the appended claims all such modificationsas fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In hydraulic servo-mechanism having pilotcontrolled motor means forregulating a condition with a signal output member connected to positionthe pilot, the combination of a conditionresponsive device having meansexerting a first force on the signal output member proportional to thecondition being controlled, first expansible chamber means connected toexert on the signal output member a force in opposition to said firstforce, and hydraulic stabilizing means comprising a liquid-filledhousing defining an intermediate chamber and upper and lower endchambers respectively, conduit means connecting said intermediatechamber with said first expansible chamber, said lower and chamberhaving an espansible wall member whereby the volume thereof may vary andopposed spring means acting on said ex pansible wall member to define aneutral position corresponding to a normal steady-state value of thevolume thereof, said hydraulic stabilizer housing having a portestablishing free communication between the intermediate chamber andsaid eXpansible lower end chamber, a reciprocable feed-back pistonmember in the upper portion of the stabilizer housing and separating theintermediate chamber irom the upper end chamber, a bypass conduit withflow restricting means communicating between the intermediate chamberand the upper end chamber, the stabilizer housing having a vent formaintaining atmospheric pressure in the upper end chamber, and feedbacklinkage means connecting the feed-back piston with the hydraulic motorwhereby movement of the motor causes motion of. the feed-back piston toproduce a hydraulic restoring efiect on the signal output member, asmodified by said restricted bypass conduit and said expansible lower endchamber.

2. In hydraulic servo-mechanism having pilotcontrolled motor means forregulating a condition with a signal output member connected to positionthe pilot, the combination of a conditionresponsive device includingmeans exerting a first force on the signal output member proportional tothe condition being controlled, means defining a first eXpansiblechamber and including a member connected to exert a force on the signaloutput member in opposition to said first force, and hydraulicstabilizing means including a liquidfilled housing with walls defining asecond cham her having a first expansible wall member whereby the volumeof the second chamber may be caused to vary, spring means acting on saidexpansible wall member to define a neutral position corresponding to anormal steady-state value of the volume of the second chamber, firstconduit means connecting the second chamber with said first expansiblechamber, a reciprocable feedback piston member disposed to form a secondmovable wall of said second chamber, a bypass conduit with flowrestricting means communicating between the second chamber and a thirdend chamber defined by the stabilizer housing at the side of said pistonremote from the second chamher, the stabilizer housing having vent meansfor maintaining substantially ambient pressure in said third chamber,and feed-back linkage means connecting the feed-back piston with thehydraulic motor whereby movement of the motor eil'ects movement of thepiston to produce a hydraulic restoring efiect on said signal outputmember, as modified by said restricted bypass conduit and said secondexpansible chamber.

3. Hydraulic servo-mechanism in accordance with claim 2 and including atleast two springbiased check-valves in the feed-back piston, one beingadapted to pass liquid from the second to the third chamber in thehydraulic stabilizer when the pressure in the second chamber reaches apreselected maximum value, the other check valve being adapted to passliquid from the third to the second chamber when the pressure in thesecond chamber reaches a preselected minimum value, to effect automaticinterchange of liquid between said second and third chambers forincreasing the rate of response of the servo-mechanism in the event ofrapid changes in the condition sensed.

4. In hydraulic servo-mechanism having pilotcontrolled motor means forregulating a condition, the combination of a signal output memberconnected to position the pilot, a condition-' responsive deviceexerting a force on the signal output member proportional to thecondition being controlled, means defining a first expansible chamberand including a member connected to exert a force on the signal outputmember in opposition to said condition-responsive force, and hydraulicstabilizing means including a liquidfilled housing with walls defining asecond chamber with a first expansible wall member adapted to vary thevolume of said second chamber, spring means acting on said expansiblewall member to define a neutral position thereof corresponding to anormal steady-state value of the volume of the second chamber, firstconduit means connecting the second chamber with the first expansiblechamber, a reciprocable feedback piston member disposed for verticalmovement and forming a second upper movable wall of the second chamber,the housing defining a third chamber above said feed-back piston, bypassconduit means including a flow restricting device communicating betweensaid second and third chambers, vent means for maintaining substantiallyambient pressure on the liquid in the third chamber, feed-back linkagemeans connecting the feed-back piston with the hydraulic motor, wherebymovement of the motor effects movement of the piston to produce ahydraulic restoring efiect on said signal output member, the feed-backpiston having at least two pressure relief valves, one adapted tointerchange liquid between said second and third chambers when thepressure in the second chamber reaches a preselected maximum value, theother relief valve being adapted to efiect interchange of liquid betweenthe second and third chambers when the pressure in the second chamberfalls to a preselected minimum value, whereby interchange of liquidbetween said second and third chambers is automatically eifected in theevent of excessive pressure changes in the second chamber.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,959,889 Wiinsch May 22, 1934 2,077,384 Dettenborn Apr. 20,1937 2,149,390 Donaldson, Jr. Mar. 7, 1939 2,251,729 Bach Aug. 5, 19412,320,508 Burns et al June 1, 1943 2,372,345 Temple Mar. 27, 19452,427,235 Smoot Sept. 9, 1947

